/*
 * @(#)CombiningAlgFactory.java
 *
 * Copyright 2003-2006 Sun Microsystems, Inc. All Rights Reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *   1. Redistribution of source code must retain the above copyright notice,
 *      this list of conditions and the following disclaimer.
 * 
 *   2. Redistribution in binary form must reproduce the above copyright
 *      notice, this list of conditions and the following disclaimer in the
 *      documentation and/or other materials provided with the distribution.
 *
 * Neither the name of Sun Microsystems, Inc. or the names of contributors may
 * be used to endorse or promote products derived from this software without
 * specific prior written permission.
 * 
 * This software is provided "AS IS," without a warranty of any kind. ALL
 * EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES, INCLUDING
 * ANY IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE
 * OR NON-INFRINGEMENT, ARE HEREBY EXCLUDED. SUN MICROSYSTEMS, INC. ("SUN")
 * AND ITS LICENSORS SHALL NOT BE LIABLE FOR ANY DAMAGES SUFFERED BY LICENSEE
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package org.wso2.balana.combine;

import org.wso2.balana.PolicyMetaData;
import org.wso2.balana.UnknownIdentifierException;
import org.wso2.balana.XACMLConstants;

import java.net.URI;

import java.util.HashMap;
import java.util.Set;

/**
 * Provides a factory mechanism for installing and retrieving combining
 * algorithms.
 * 
 * @since 1.0
 * @author Seth Proctor
 */
public abstract class CombiningAlgFactory {

	// the proxy used to get the default factory
	private static CombiningAlgFactoryProxy defaultFactoryProxy;

	// the map of registered factories
	private static HashMap<String, CombiningAlgFactoryProxy> registeredFactories;

	/**
	 * static initializer that sets up the default factory proxy and registers
	 * the standard namespaces
	 */
	static {
		CombiningAlgFactoryProxy proxy = new CombiningAlgFactoryProxy() {
			public CombiningAlgFactory getFactory() {
				return StandardCombiningAlgFactory.getFactory();
			}
		};

		registeredFactories = new HashMap<String, CombiningAlgFactoryProxy>();
		registeredFactories.put(XACMLConstants.XACML_1_0_IDENTIFIER, proxy);
		registeredFactories.put(XACMLConstants.XACML_2_0_IDENTIFIER, proxy);
		registeredFactories.put(XACMLConstants.XACML_3_0_IDENTIFIER, proxy);

		defaultFactoryProxy = proxy;
	};

	/**
	 * Default constructor. Used only by subclasses.
	 */
	protected CombiningAlgFactory() {

	}

	/**
	 * Returns the default factory. Depending on the default factory's
	 * implementation, this may return a singleton instance or new instances
	 * with each invocation.
	 * 
	 * @return the default <code>CombiningAlgFactory</code>
	 */
	public static final CombiningAlgFactory getInstance() {
		return defaultFactoryProxy.getFactory();
	}

	/**
	 * Returns a factory based on the given identifier. You may register as many
	 * factories as you like, and then retrieve them through this interface, but
	 * a factory may only be registered once using a given identifier. By
	 * default, the standard XACML 1.0 2.0 and 3.0 identifiers are registered to
	 * provide the standard factory.
	 * 
	 * @param identifier
	 *            the identifier for a factory
	 * 
	 * @return a <code>CombiningAlgFactory</code>
	 * 
	 * @throws UnknownIdentifierException
	 *             if the given identifier isn't registered
	 */
	public static final CombiningAlgFactory getInstance(String identifier)
			throws UnknownIdentifierException {

		CombiningAlgFactoryProxy proxy = registeredFactories.get(identifier);
		if (proxy == null) {
			throw new UnknownIdentifierException("Unknown CombiningAlgFactory "
					+ "identifier: " + identifier);
		}
		return proxy.getFactory();
	}

	/**
	 * Sets the default factory. This does not register the factory proxy as an
	 * identifiable factory.
	 * 
	 * @param proxy
	 *            the <code>CombiningAlgFactoryProxy</code> to set as the new
	 *            default factory proxy
	 */
	public static final void setDefaultFactory(CombiningAlgFactoryProxy proxy) {
		defaultFactoryProxy = proxy;
	}

	/**
	 * Registers the given factory proxy with the given identifier. If the
	 * identifier is already used, then this throws an exception. If the
	 * identifier is not already used, then it will always be bound to the given
	 * proxy.
	 * 
	 * @param identifier
	 *            the identifier for the proxy
	 * @param proxy
	 *            the <code>CombiningAlgFactoryProxy</code> to register with the
	 *            given identifier
	 * 
	 * @throws IllegalArgumentException
	 *             if the identifier is already used
	 */
	public static final void registerFactory(String identifier,
			CombiningAlgFactoryProxy proxy) throws IllegalArgumentException {
		synchronized (registeredFactories) {
			if (registeredFactories.containsKey(identifier))
				throw new IllegalArgumentException("Identifier is already "
						+ "registered as " + "CombiningAlgFactory: "
						+ identifier);

			registeredFactories.put(identifier, proxy);
		}
	}

	/**
	 * Adds a combining algorithm to the factory. This single instance will be
	 * returned to anyone who asks the factory for an algorithm with the id
	 * given here.
	 * 
	 * @param alg
	 *            the combining algorithm to add
	 * 
	 * @throws IllegalArgumentException
	 *             if the algorithm is already registered
	 */
	public abstract void addAlgorithm(CombiningAlgorithm alg);

	/**
	 * Adds a combining algorithm to the factory. This single instance will be
	 * returned to anyone who asks the factory for an algorithm with the id
	 * given here.
	 * 
	 * @deprecated As of version 1.2, replaced by
	 *             {@link #addAlgorithm(CombiningAlgorithm)}. The new factory
	 *             system requires you to get a factory instance and then call
	 *             the non-static methods on that factory. The static versions
	 *             of these methods have been left in for now, but are slower
	 *             and will be removed in a future version.
	 * 
	 * @param alg
	 *            the combining algorithm to add
	 * 
	 * @throws IllegalArgumentException
	 *             if the algorithm is already registered
	 */
	public static void addCombiningAlg(CombiningAlgorithm alg) {
		getInstance().addAlgorithm(alg);
	}

	/**
	 * Returns the algorithm identifiers supported by this factory.
	 * 
	 * @return a <code>Set</code> of <code>String</code>s
	 */
	public abstract Set getSupportedAlgorithms();

	/**
	 * Tries to return the correct combinging algorithm based on the given
	 * algorithm ID.
	 * 
	 * @param algId
	 *            the identifier by which the algorithm is known
	 * 
	 * @return a combining algorithm
	 * 
	 * @throws UnknownIdentifierException
	 *             algId is unknown
	 */
	public abstract CombiningAlgorithm createAlgorithm(URI algId)
			throws UnknownIdentifierException;

	/**
	 * Tries to return the correct combinging algorithm based on the given
	 * algorithm ID.
	 * 
	 * @deprecated As of version 1.2, replaced by {@link #createAlgorithm(URI)}.
	 *             The new factory system requires you to get a factory instance
	 *             and then call the non-static methods on that factory. The
	 *             static versions of these methods have been left in for now,
	 *             but are slower and will be removed in a future version.
	 * 
	 * @param algId
	 *            the identifier by which the algorithm is known
	 * 
	 * @return a combining algorithm
	 * 
	 * @throws UnknownIdentifierException
	 *             algId is unknown
	 */
	public static CombiningAlgorithm createCombiningAlg(URI algId)
			throws UnknownIdentifierException {
		return getInstance().createAlgorithm(algId);
	}

}
